Dipole locator using multiple measurement points

ABSTRACT

A receiver and tracking system for identifying a location of a magnetic field source. In a preferred embodiment a plurality of tri-axial antennas are positioned at three distinct points on a receiver frame. Each antenna detects a magnetic field from a source and a processor is used to determine a location of the source relative to the frame using the antenna signals. Each tri-axial antenna comprises three windings in each of three channels defined by a support structure. The windings each define an aperture area. The windings have substantially identical aperture areas and have a common center point. The receiver may to display to the operator the relative location of the field source or may direct the operator to a spot directly above the field source.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/589,141, filed Jan. 5, 2015, which is a continuation of U.S.patent application Ser. No. 13/458,134, filed Apr. 27, 2012, now U.S.Pat. No. 8,928,323, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/844,886, filed Jul. 28, 2010, now U.S. Pat. No.8,497,684, which is a continuation of U.S. patent application Ser. No.11/382,644, filed May 10, 2006, now U.S. Pat. No. 7,786,731, issued Aug.31, 2010, which claims the benefit of U.S. Provisional PatentApplication No. 60/728,066, filed Oct. 19, 2005 and U.S. ProvisionalPatent Application No. 60/680,780, filed May 13, 2005, the contents ofwhich are incorporated fully herein by reference.

FIELD

The present invention relates generally to the field of locatingunderground objects, and in particular to locating and tracking a beaconwithin the field of operation of a horizontal drilling machine.

SUMMARY

The present invention is directed to an antenna arrangement comprising asupport member, and a first, second, third, fourth, fifth, and sixthwindings. The support member comprises a first channel, a secondchannel, and a third channel. The first channel is disposed in a firstaxis, the second channel is disposed in a second axis, and the thirdchannel is disposed in a third axis. The first winding is supported inthe first channel. The fourth winding is supported in the first channeland wound opposite the first winding. The second winding is supported inthe second channel. The fifth winding is supported in the second channeland wound opposite the second winding. The third winding is supported inthe third channel. The sixth winding is supported in the third channeland wound opposite the third winding. The first winding and the fourthwinding define an aperture area, the second winding and the fifthwinding define an aperture area, and the third winding and the sixthwinding define an aperture area. The aperture area of each winding isthe same and the windings have a common center point.

The present invention is also directed to an antenna arrangementcomprising a first antenna coil, a second antenna coil, and a thirdantenna coil. The second antenna coil circumvents the first antenna coiland the third antenna coil circumvents the second antenna coil. Thefirst antenna coil, the second antenna coil, and the third antenna coilhave a common center point, and each of the antenna coils comprise afirst winding wound in a first direction and a second winding woundopposite the first winding.

The present invention is further directed to an antenna arrangementcomprising a first antenna, a second antenna, and a third antenna. Thesecond antenna circumvents the first antenna and the third antennacircumvents the second antenna. The first antenna, the second antenna,and the third antenna have a common center point and each of theantennas comprise a first printed circuit board and a second printedcircuit board facing opposite the direction of the first printed circuitboard to induce current flow in a direction opposite the first printedcircuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a horizontal directional drilling systemfor drilling a horizontal borehole and a tracking system built inaccordance with the present invention.

FIG. 2 is a perspective view of a receiver assembly of the trackingsystem of FIG. 1 constructed in accordance with the present invention.

FIG. 3 is a perspective, partially cut-away view of a support structurefor an antenna arrangement for use with the present invention.

FIG. 4 is a perspective, partially cut-away view of the antennaarrangement from FIG. 3.

FIG. 5 shows an alternative embodiment for an antenna arrangement foruse with the present invention.

FIG. 5A is a perspective view of an alternative embodiment of an antennaarrangement.

FIG. 6 is a block diagram of a tracking system constructed to detect andprocess signals from a magnetic field source.

FIG. 7 is a geometric representation of the relationship between theantenna arrangements of a receiver assembly built in accordance with thepresent invention.

FIG. 8 is a geometric representation of the relationship between amagnetic field source and the antenna arrangement of a tracking systembuilt in accordance with the present invention.

FIG. 9 is representative visual display for a preferred embodiment ofthe present invention.

FIG. 10 is a graphical representation of total magnetic field readingsfrom a magnetic field source as detected by a receiver assembly in they-z plane.

FIG. 11 is a graph showing the field readings of FIG. 9 in the y-zplane.

FIG. 12 is an illustration of flux lines radiating from a magnetic fieldsource transmitter, as depicted in the x-y plane.

FIG. 13 is a geometrical representation of the relationship between amagnetic field source transmitter and a tilted receiver assembly.

FIG. 14 is a perspective view of an alternative embodiment of theantenna arrangement for use with the present invention.

FIG. 14A is a perspective view of an alternative embodiment of anantenna arrangement.

FIG. 15 is a perspective view of another alternative embodiment of theantenna arrangement for use with the present invention.

FIG. 16 is a perspective view of the antenna arrangement of FIG. 15supported within a frame and having a ferrite rod antenna.

BACKGROUND

The horizontal directional drilling (“HDD”) industry traditionally useswalk-over tracking techniques to follow the progress of a bore, to findthe surface location immediately above the drill bit, and to determinethe depth of the drill bit from that surface location. The primarytracking tools are a subsurface transmitter and a hand-carried surfacereceiver. The transmitter, located in or very near a boring tool,generally emits a magnetic dipole field created by a single coil dipoleantenna. The transmitted dipole field can be used for both location andcommunication with the above ground receiver.

Conventional receivers often contain an arrangement of three antennasmounted in each of the three Cartesian axes. When the antennaarrangement senses the dipole field, the output of each antenna isproportional to the magnitude of the magnetic flux density as detectedalong the axis of the particular antenna. The signals from the antennasare mathematically resolved to provide information about the relativelocation of the boring tool. The process of locating the dipole, andthus the boring tool, currently involves two steps: determining itslocation along the z-axis (fore and aft) and then along the y-axis (leftand right). One skilled in the art will appreciate a receiver can locatea transmitter in the fore-aft direction (along the z-axis) using theamplitude and phase of the transmitter's generated horizontal andvertical field components as measured in the vertical plane normal tothe surface and extending through the transmitter axis (the x-z plane).A receiver can also determine the location of a single transmitter inthe left-right directions using the amplitude and phase of the dipolefield in the horizontal plane (the y-z plane). However, the left-rightdetermination can only be used either in front of or behind thetransmitter because there is no y component to the dipole field when thereceiver is directly above the transmitter (such that z=0). Thereremains a need for improved tracking systems for simultaneously locatingthe transmitter in both the fore-aft and left-right directions with anantenna arrangement positioned directly over the transmitter.

DETAILED DESCRIPTION

With reference now to the drawings in general, and FIG. 1 in particular,there is shown therein a HDD system 10 for use with the presentinvention. FIG. 1 illustrates the usefulness of HDD by demonstratingthat a borehole 12 can be made without disturbing an above-groundstructure, namely a roadway or walkway as denoted by reference numeral14. To cut or drill the borehole 12, a drill string 16 carrying a drillbit 18 is rotationally driven by a rotary drive system 20. When the HDDsystem 10 is used for drilling a borehole 12, monitoring the position ofthe drill bit 18 is critical to accurate placement of the borehole andsubsequently installed utilities. The present invention is directed to asystem 22 and method for tracking and monitoring a downhole toolassembly 24 during a horizontal directional drilling operation.

The HDD system 10 of the present invention is suitable fornear-horizontal subsurface placement of utility services, for exampleunder the roadway 14, building, river, or other obstacle. The trackingsystem 22 is particularly suited for providing an accuratethree-dimensional locate of the downhole tool assembly 24 from anyposition above ground. The locating and monitoring operation with thepresent tracking system 22 is advantageous in that it may beaccomplished in a single operation. The present invention also permitsthe position of the downhole tool assembly 24 to be monitored withoutrequiring the tracking system 22 be placed directly over a transmitterin the downhole tool assembly. These and other advantages associatedwith the present invention will become apparent from the followingdescription of the preferred embodiments.

With continued reference to FIG. 1, the HDD system 10 comprises thedrilling machine 28 operatively connected by the drill string 16 to thedownhole tool assembly 24. The downhole tool assembly 24 preferablycomprises the drill bit 18 or other directional boring tool, and anelectronics package 30. The electronics package 30 comprises atransmitter 32 for emitting a signal through the ground. Preferably thetransmitter 32 comprises a dipole antenna that emits a magnetic dipolefield. The electronics package 30 may also comprise a plurality ofsensors 34 for detecting operational characteristics of the downholetool assembly 24 and the drill bit 18. The plurality of sensors 34 maygenerally comprise sensors such as a roll sensor to sense the rollposition of the drill bit 18, a pitch sensor to sense the pitch of thedrill bit, a temperature sensor to sense the temperature in theelectronics package 30, and a voltage sensor to indicate battery status.The information detected by the plurality of sensors 34 is preferablycommunicated from the downhole tool assembly 24 on the signaltransmitted by the transmitter 32 using modulation or other knowntechniques.

With reference now to FIG. 2, shown therein is an embodiment of thetracking system 22 of the present invention. The tracking system 22comprises a receiver assembly 36. The receiver assembly 36 comprises aframe 38, a computer processor 40, and a plurality of antennaarrangements 42 supported by the frame. The processor 40 is supported onthe frame 38 and operatively connected to the plurality of antennaarrangements 42. The frame 38 is preferably of lightweight constructionand capable of being carried by an operator using a handle 47. In apreferred embodiment, the receiver assembly 36 also comprises a visualdisplay 46 and a battery 48 for providing power to the various parts ofthe receiver assembly. The visual display 46 may be adapted to provide avisual representation of the tracking system 22 relative to the drillbit 18 and other information useful to the operator. The receiverassembly 36 may also comprise a transmitting antenna (not shown) fortransmitting information from the receiver assembly to the drillingmachine 28 or other remote system (not shown).

The antenna arrangements 42 are supported on the frame 38 and separatedfrom each other by a known distance and in known relative positions. Oneskilled in the art will appreciate the separation and relative positionof the antenna arrangements 42 may be selected based on the number ofantenna arrangements and antenna design, size, and power. In theembodiment of FIG. 2, the plurality of antenna arrangements 42 comprisesa first 42 a, a second 42 b, and a third 42 c antenna arrangement.Preferably, the antenna arrangements 42 are mounted in a plane and atthe vertexes of an equilateral triangle. One skilled in the art willappreciate a greater distance or spread between the antennas willprovide better resolution and accuracy. A workable compromise betweenspread and physical size has been found to be a separation distance ofat least 18 inches. Other receiver configurations are possible, as longas each antenna arrangement 42 is capable of isolating the magneticfield in each of the Cartesian axes at the point on the frame 38 wherethe antenna is positioned. For example, the invention contemplates afourth antenna arrangement that may be supported by the frame 38 atposition either above or below the plane formed by the first 42 a,second 42 b, and third 42 c antenna arrangements.

Each of the plurality of antenna arrangements 42 is preferably atri-axial antenna. Each antenna arrangement 42 is adapted to measure thetotal magnetic field at its respective position on the frame 38. Eachantenna arrangement 42 may comprise three orthogonal antennas whichmeasure the magnetic field along their specific axis of sensitivity.Each of the three orthogonal antenna signals is squared, summed, andthen the square root is taken to obtain the total field. Thiscalculation assumes the sensitivities of each antenna are the same andthat the center of each antenna is coincident with the other two suchthat the antenna arrangement is measuring the total field at a singlepoint in space.

Referring now to FIGS. 3 and 4, there is shown therein the preferredembodiment for an antenna arrangement 42 for use with the presentinvention. The antenna arrangement 42 comprises a support structure 50defining three channels 52. The support structure 50 is preferablyformed of lightweight plastic. For ease of construction, the structure50 may be manufactured in at least two parts that are secured together.The structure 50 is preferably manufactured in such a way that threechannels 52 are each dimensionally identical. More preferably, thesupport structure 50 has a substantially cubical shape and each of thethree channels 52 defines a rectangular aperture area having a centerpoint. Most preferably, the channels 52 are mutually orthogonal andoriented so that the center points are coincident.

The channels 52 are orthogonally oriented such that a first channel 52 ais circumvented by a second channel 52 b, and a third channel 52 ccircumvents the first channel and the second channel. A preferredembodiment for such an arrangement comprises an orientation where a longside of the rectangular second channel 52 b is adjacent to andperpendicular to a short side of the rectangular first channel 52 a, anda diagonal of the rectangular third channel 52 c is substantiallycoincident with a plane formed by the rectangular second channel. Thesize of the antenna 42 can be optimized by designing the channels 52such that the diagonal of the third channel 52 c intersects the plane ofthe second channel 52 b at an angle of between 0-10 degrees. Thediagonal of the third channel 52 c will intersect the plane of thesecond channel 52 b at an angle of approximately 4 degrees.

Shown in FIG. 4, the antenna arrangement 42 further comprises threeantenna coils 54. The coils 54 are preferably insulated windings ofmagnet wire. The three coils 54 are separately wound around thestructure 50, one in each of the three channels 52 a, 52 b, and 52 c, toform three coil loops 54 a, 54 b, and 54 c. Because of the orientationof the channels 52 a, 52 b, and 52 c, as previously described, the coils54 a, 54 b, and 54 c do not intersect each other when positioned in thechannels. Preferably, the coils 54 comprise approximately 100 turns ofmagnet wire, though other numbers of turns may be used depending on wiresize and antenna sensitivity or other design considerations. Due to thechannel configuration, the coil loops 54 all have coincident centerpoints, and their sensitivities are substantially identical. The coilloops 54 also define substantially identical aperture areas and haverounded corners. Since the coils 54 are wound with magnet wire, theirresistances are relatively low. Therefore, the antenna 42 can be tunedproperly to increase its sensitivity, thus allowing the receiver 36(FIG. 2) to detect the magnetic field from greater depths.

The present invention also contemplates other embodiments for theantenna arrangement 42, including use of traditional ferrite rodantennas. For example, though not shown, the antenna arrangement 42could comprise three ferrite rod antennas in orthogonal relationship.However, the antenna arrangement 42 having coil windings 54 shown inFIG. 4 has significant advantages over the use of traditional ferriterod antennas. Ferrite rods greatly enhance the sensitivity of theantenna, thus enabling the receiver to work to deeper depths. However,the ferrite properties are not constant over a temperature range. If ahigh level of accuracy is required, the drift over the temperature rangeexperienced on work sites is unacceptable. Also, the center of eachantenna would obviously not be coincident with the center of the otherantennas. This will introduce errors in the total field calculation.

Referring now to FIG. 5, there is shown therein an alternativeembodiment for the antenna arrangement 55 for use with the presentinvention. As shown in FIG. 5, the antenna arrangement 55 comprisesthree tri-axial antennas made of printed circuit boards 56 (PCBs).Preferably, the PCBs 56 are supported on a mount 58 and configured as acuboid. In a cuboid configuration, opposite PCBs 56 are connected inseries. The PCBs 56 are preferably comprised of many connected layers,allowing the winds to be connected in series to increase the number ofturns, and therefore the inductance of the antennas. When configured asa cuboid, the PCBs 56 antennas can be mounted such that their respectiveaxes are perpendicular and a geometric center of the antenna arrangement55 will not change as the antenna arrangement is maneuvered.

Using PCBs 56 for the antenna arrangement 55 also has advantages. Thecuboid arrangement of the PCBs 56 allows the observation point forcalculation of the total field sensed by the antenna arrangement 55 toremain at the geometric center of the antenna. Additionally, as PCBs aremanufactured by precision machines, tolerances associated with manuallywrapping the loops are reduced. The antennas produced in this fashionare very uniform from one board to the next. Higher precisionmeasurements may be possible with this configuration.

Referring now to FIG. 5A, an alternative antenna arrangement is shown.FIG. 5A shows an antenna arrangement 55A. The antenna arrangement 55Acomprises a first antenna 57A, a second antenna 57B, and a third antenna57C. Each of the antennas 57A, 57B, and 57C comprise a first PCB 59A anda second PCB 59B. The first PCB 59A faces opposite the direction of thesecond PCB 59B to induce current flow in a direction opposite the firstPCB. This positioning creates a differential antenna to help increasethe accuracy of the antenna arrangement 55A. The antennas 57A, 57B, and57C shown in FIG. 5A may comprise the same dimensions or differentdimensions.

Continuing with FIG. 5A, the first PCB 59A and the second PCB 59B eachcomprise a front side 61A and a back side 61B. The back side 61B of thefirst PCB 59A is shown adjacent to the back side 61B of the second PCB59B, allowing the first PCB and the second PCB to face oppositedirections. The first PCB 59A and the second PCB 59B may be connected bysupport structures 63. The support structures 63 hold the antennas 57A,57B, and 57C in place such that the second antenna 57B circumvents thefirst antenna 57A, and the third antenna 57C circumvents the secondantenna 57B. The antennas 57A, 57B, and 57C shown in FIG. 5A all have acommon center point and are mutually orthogonal. The antennas 57A, 57B,and 57C shown in FIG. 5A are a substantially rectangular shape; however,the antennas may form different shapes or dimensions if needed. Each ofthe PCBs 59A and 59B shown in FIG. 5A have an opening in the center;however, each of the PCBs may also be formed as a solid piece with noopenings in the center.

The antennas 57A, 57B, and 57C shown in FIG. 5A may be modified to onlycomprise one PCB each. Each PCB may comprise a plurality of connectedlayers. The layers may be formed such that a portion of the layersinduce current flow in a first direction and a second portion of thelayers induce current flow in a second direction opposite the firstdirection. Like the embodiment shown in FIG. 5A, this positioningcreates a differential antenna to increase the accuracy of the antennaarrangement 55A.

With reference now to FIG. 6, shown therein is a block diagram of apreferred embodiment of the receiver assembly 36 of the presentinvention. The antenna arrangements 42, as described earlier, measure achange in the magnetic field. A change in the magnetic field sensed willresult in a voltage being induced in response to the transmitter'smagnetic field. The voltages from the antennas 42 are sent to filters 60and amplifiers 62. Filters 60 eliminate the effects of other signalsreceived by the antennas 42 from local noise sources. Amplifiers 62increase the signal received by the antennas 42. An A/D converter 64 isused to convert analog waveform information into digital data.

The digital data from the A/D converter 64 is then sent to a centralprocessor 66 (CPU) to calculate the location of the transmitter 32relative to the receiver assembly 36. The CPU 66 may comprise a digitalsignal processor (DSP) and a microcontroller. The CPU 66 decodes theinformation from the A/D converter 64 and performs calculations todetermine the location of the transmitter in a manner yet to bedescribed. The CPU 66 may also discern information transmitted on themagnetic field, to determine the battery status, pitch, roll, and otherinformation about the downhole tool assembly 24.

The receiver assembly 36 may also comprise one or more sensors 68 usedto sense operational information about the receiver assembly 36. Forexample, one or more accelerometers, or other known inclination andorientation sensors or magnetic compasses, may provide informationconcerning the roll or tilt of the receiver 36. Information from thesensors 68 is provided to the A/D converter 64 and to the CPU 66 wherethe DSP may make calculations to compensate for the receiver 36 notbeing level.

The receiver assembly 36 further comprises a user interface 70 having aplurality of buttons, joysticks, and other input devices. The operatorcan input information for use by the CPU 66 through the user interface70. Information entered through the user interface 70 or determined orused by the CPU 66 may be displayed to the operator on a visual display72 screen. The receiver assembly 36 also comprises a radio antenna 74for transmitting information from the CPU 66 to a remote unit, such asat the drilling machine 10.

The receiver assembly 36 is preferably powered by a battery assembly 76and power regulation system 78. The battery assembly 76 may comprisemultiple D-cell sized batteries, though other sources are contemplated,such as rechargeable batteries. The power regulation system 78 maycomprise a linear regulator or switch mode regulator to provide power tothe various components of the receiver 36.

The receiver assembly 36 of the present invention uses multiple pointsof measurement, at the plurality of antenna arrangements 42, toaccurately locate the transmitter 32 in three-dimensional (3-D) space.Each antenna arrangement 42 obtains three distinguishable orthogonalcomponents of a magnetic field available at any position. In thepreferred embodiment described above, the three antennas 42 a, 42 b, and42 c, provide those magnetic field measurements.

Referring now to FIGS. 7 and 8, shown therein are the relationship ofthe antenna arrangements 42 to the transmitter 32 and the geometriesinvolved. With three points of measurements from the antennas 42, thelocation of the transmitter 32 can be found in 3-D space by the receiverassembly 36 at any point on the ground using the equations below.

The Dipole Equations for the Null Field, the field perpendicular to theearth's surface, and Total Field are:

$\begin{matrix}{B_{x} = {k \cdot \frac{{3 \cdot z^{2}} - r^{2}}{r^{5}}}} & (1) \\{B_{y} = {3{k \cdot \frac{y \cdot z}{r^{5}}}}} & (2) \\{B_{z} = {3\;{k \cdot \frac{x \cdot z}{r^{5}}}}} & (3) \\{B_{T} = {k \cdot \frac{\sqrt{{3 \cdot z^{2}} + r^{2}}}{r^{4}}}} & (4)\end{matrix}$where r²=x²+y²+z², and k is a calibration constant. These equationsassume that the receiver 36 is flat (x₁=x₂=x₃=x) and above thetransmitter 32 (x>0). However, one skilled in the art will appreciatethe ability to account for tilt of the receiver 36 with informationreceived from the sensors 68 and the pitch of the transmitter 32 withinformation received from the downhole tool assembly 24.

Referring to FIG. 7, the equations relating each of the points ofmeasurement (at the antennas 42 a, 42 b, and 42 c) on the receiver 36 to(x, y, z) are:

$\begin{matrix}{y_{1} = {y + {\frac{\sqrt{3}}{3} \cdot L \cdot {\cos\left( {\frac{\pi}{6} + \gamma} \right)}}}} & {z_{1} = {z + {\frac{\sqrt{3}}{3} \cdot L \cdot {\sin\left( {\frac{\pi}{6} + \gamma} \right)}}}} & \left( {4a} \right) \\{y_{2} = {y - {\frac{\sqrt{3}}{3} \cdot L \cdot {\cos\left( {\frac{\pi}{6} - \gamma} \right)}}}} & {z_{2} = {z + {\frac{\sqrt{3}}{3} \cdot L \cdot {\sin\left( {\frac{\pi}{6} - \gamma} \right)}}}} & \left( {4b} \right) \\{y_{3} = {y + {\frac{\sqrt{3}}{3} \cdot L \cdot {\sin(\gamma)}}}} & {z_{3} = {z - {\frac{\sqrt{3}}{3} \cdot L \cdot {\cos(\gamma)}}}} & \left( {4c} \right)\end{matrix}$Also, it can be seen from FIG. 8 that

${\cos\;\theta_{1}} = \frac{z_{1}}{r_{1}}$or z₁=r₁·cos θ₁. The same is true for the other points, so in generalz_(i)=r_(i)·cos θ_(i).

Adjusting for a tilted receiver 36, the rotated coordinate system givesthe following: (note that the {right arrow over (y)} axis is unaffected){right arrow over (z)}′={right arrow over (z)} cos P+{right arrow over(x)} sin P {right arrow over (x)}′=−{right arrow over (z)} sin P+{rightarrow over (x)} cos Pz′=z cos P+x sin P x′=−z sin P+x cos P

Solving for B_({right arrow over (x)}):

$B_{{\overset{\rightarrow}{x}}^{\prime}} = {{3{k \cdot \frac{x^{\prime} \cdot z^{\prime}}{r^{5}}}{\overset{\rightarrow}{x}}^{\prime}} + {{k \cdot \frac{{3 \cdot z^{\prime\; 2}} - r^{2}}{r^{5}}}{{\overset{\rightarrow}{z}}^{\prime}.}}}$Plugging in the rotated values and simplifying gives:

$B_{\overset{\rightarrow}{x}} = {{k \cdot \frac{{{3 \cdot x^{2} \cdot \sin}\; P} + {{3 \cdot x \cdot z \cdot \cos}\; P} - {{r^{2} \cdot \sin}\; P}}{r^{5}}}{\overset{\rightarrow}{x}.}}$

These equations provide measurable parameters regardless of pitch, andthe system of equations can be written as follows:

$\begin{matrix}{B_{\overset{\rightarrow}{x},i} = {k \cdot \frac{{{3 \cdot x^{2} \cdot \sin}\; P} + {{3 \cdot x \cdot z_{i} \cdot \cos}\; P} - {{r_{i}^{2} \cdot \sin}\; P}}{r_{i}^{5}}}} & \left( {{3\mspace{14mu}{equations}},{i = 1},2,3} \right) \\{B_{T,i} = {k \cdot \frac{\sqrt{{3 \cdot \left( {{z_{i}\cos\; P} + {x\;\sin\; P}} \right)^{2}} + r_{i}^{2}}}{r_{i}^{4}}}} & \left( {{3\mspace{14mu}{equations}},{i = 1},2,3} \right)\end{matrix}$

There are now six equations (B_({right arrow over (x)},1),B_({right arrow over (x)},2), B_({right arrow over (x)},3), B_(T,1),B_(T,2), B_(T,3)) and five unknowns (x, y, z, k, γ) and the system canbe solved with any number of known methods. One skilled in the art willappreciate that since k is determined from the above equations, there isno calibration required to use this system.

The present invention can therefore be used to identify the exactcoordinates of the receiver assembly 36 relative to the transmitter 32using the magnetic field measurements from the plurality of antennaarrangements 42 and the equations above. The present invention can beused to identify the location of the transmitter 32 in 3-D space withoutany additional movements, as long as the magnetic field from thetransmitter can be detected by the plurality of antenna arrangements 42.The information concerning the location of the transmitter 32 ispreferably provided to the operator using the visual display 72.

There is shown in FIG. 9 a preferred configuration of a screen display72. The drill string 16 is shown underground. The x-, y-, andz-coordinates are the distances to the downhole tool assembly 24 fromthe receiver assembly 36 location. A receiver icon is also on the gridto graphically show the relationship of the receiver assembly 36 to thetransmitter 32. Transmitter 32 temperature, battery status, pitch, roll,yaw, signal strength, signal gain, and signal frequency icons are alsoshown on the display 72 to provide a graphic and numeric representationof each. Other downhole tool 18 data or operational information couldsimilarly be displayed. This allows the downhole tool assembly 24position to be monitored and determined without requiring the receiverassembly 36 to be placed directly over the transmitter 32. All data maybe stored in memory or a database to log the history of each bore. Manyother functions may be made available thru the main menu such aschanging units, calibration mode, alternate two-dimensional view, anddemonstrations and help.

In an alternative embodiment, the receiver assembly 36 of the presentinvention can also be used with certain directed steps to take advantageof situations where the transmitter 32 strength or sensitivity of theplurality of antenna arrangements 42 does not permit the 3-D location asdescribed above. In such a case, use of the receiver assembly 36involves location of a particular spot directly behind the transmitter32 before pinpointing the location of the transmitter. However, with themultiple measurement points available at the plurality of antennaarrangements 42 of the receiver assembly 36, the receiver can easilydirect an operator to the proper spots to ease determination of thelocation of the transmitter. The alternative use involves a process ofusing the visual display 72 to first direct the operator to a positiondirectly behind and oriented in the same direction as the downhole toolassembly 24 and then to a position directly above the downhole toolassembly.

In the first step of the alternative embodiment, the operator uses thereceiver 36 to find a location where the total magnetic field readingfor each of the plurality of antenna arrangements 42 is the same and thereceiver is rotationally aligned with the transmitter 32. This step ispreferably accomplished simultaneously, using the display 72 to directthe operator to the desired location.

The spot where the magnetic field reading at each antenna arrangement 42a, 42 b, and 42 c is the same is where, from the equations above,B_(1T)=B_(2T)=B_(3T). FIGS. 10 and 11 are graphic illustrations of thetotal magnetic field readings as the receiver 36 is moved within the y-zplane for a constant depth and for a receiver rotationally aligned withthe transmitter 32 (so that γ=0). The operator can be directed to thepoint where the field strengths are the same using the readings from theplurality of antenna arrangements 42 and the following calculations.

First, calculate

${\overset{\_}{r}}_{i} = {\sqrt[3]{\frac{k}{B_{iT}}}.}$Then

${V_{1 - 2} = \frac{{\overset{\_}{r}}_{1} - {\overset{\_}{r}}_{2}}{L}},{V_{1 - 3} = \frac{{\overset{\_}{r}}_{1} - {\overset{\_}{r}}_{3}}{L}},{{{and}\mspace{14mu} V_{2 - 3}} = {\frac{{\overset{\_}{r}}_{2} - {\overset{\_}{r}}_{3}}{L}.}}$And then V_(y)=V₁₋₂ and

$V_{z} = {{{V_{2 - 3} \cdot \cos}\frac{\pi}{6}} + {{V_{1 - 3} \cdot \cos}{\frac{\pi}{6}.}}}$These vectors can be shown in two-dimensional (2-D) space to direct theoperator to the spot where the vectors are 0, whereB_(1T)=B_(2T)=B_(3T).

At the same time, the display 72 can be used to direct the operator torotate the receiver assembly 36 so that the receiver is directionallyaligned with the transmitter 32 and, consequently, the downhole toolassembly 24. One skilled in the art will appreciate that the location ofthe spot where the magnetic fields are equal at each of the plurality ofantenna arrangements 42 (B_(1T)=B_(2T)=B_(3T)) will be different if thereceiver 36 is not aligned with the transmitter 32 (when γ≠0). Thereforethe receiver 36 must be rotated properly to ensure the correct spot isfound. The receiver assembly 36 will be aligned with the transmitter 32when the flux line through the antenna arrangement 42 c at the back endof the receiver (the “rear pod”) is along the z-axis. By using thedisplay 72 to show the operator the angle at which the flux impinges therear pod 42 c, the user can align the receiver 36 with the flux linesand keep it rotated properly.

When these steps are followed and the operator is directed to the spotwhere all conditions are met, then the receiver will be located with y=0and γ=0. This spot is easily found, requires little computation, andgreatly simplifies the location process. The next step in the process isto direct the operator to move the receiver 36 to a position directlyabove the transmitter 32 to precisely locate the downhole tool assembly24.

Referring now to FIG. 12, there is shown therein a graphical depictionof flux lines radiating from the transmitter 32 in the x-z plane.Assuming the pitch of the receiver 36 is 0, note that the angle α

0 as z

0. Therefore, the receiver 36 preferably displays this angle graphicallyto the operator, and the operator can move the receiver until thiscondition is true. At this point, each of the front antenna arrangements42 a and 42 b (the “front pods”) will be located on the line where z=0,and the transmitter 32 located in between and directly below the frontpods 42 a and 42 b.

One skilled in the art will appreciate that when the magnetic field ismeasured at z=0, then

$r = {\sqrt[3]{\frac{k}{B_{T}}}.}$Since the receiver 36 is located where z=0 if the above steps have beenfollowed, then the geometry shown in FIG. 13 can be used to calculatethe depth, x, of the transmitter 32. As previously discussed, thereceiver 36 may contain sensors 68 to account for tilt of the receiverand enable the calculation of β. Then, as r₁, r₂, L, and β are knownvalues, x can be solved for through known geometry. The value for y canalso be determined in the event that the receiver 36 has been movedslightly off of the line y=0. The operator can be directed to move thereceiver until y=0 in order to be positioned to get a proper depthreading.

The process allows the receiver assembly 36 to be used to locate thedownhole tool assembly 24 quickly and accurately, with few steps andlittle computation. It should also be noted that the step for findingthe spot where the magnetic field strengths in each of the antennaarrangements 42 are equal is only necessary when the operator does nothave a relative idea of where the transmitter 32 is located. If thegeneral location of the downhole tool assembly 24 is known, then theoperator can use the receiver 36 to find the line where z=0, and thenthe depth of the transmitter 32.

With the present invention, improved methods for directing and drillinga horizontal directional borehole 12 are also possible. For example,trackers and beacons used for directional drilling generally do notindicate how much the drill bit is moving as an HDD system 10 is used tomake steering corrections to redirect the borehole 12. Currently,steering corrections are dependent on machine operators' expertise. Thepresent invention removes the uncertainty of operators' guesswork. Withthe present invention, the receiver 36 can indicate at any given pointin time the precise relative location of the downhole tool assembly 24and the drilling bit 18.

In an improved method for boring, the receiver assembly 36 can be set onthe ground with a centerline of the receiver directly on the desiredpath for the borehole 12. The display 72 can then be used to provide theoperator with immediate feedback of the location and heading of thedrill bit 18 relative to the desired path.

A method for creating a horizontal directional borehole 12 in the earthis also accomplished with the following steps. First, the receiverassembly 36 is placed on the ground in the proximity of the drill bit 18with the longitudinal display axis of the receiver assembly aligned withthe desired bore path 12. As the drill bit 18 is advanced forwardwithout rotation to perform a steering correction in the horizontalplane, an image of the orientation of the drill bit relative to thereceiver assembly 36 can be transmitted from the receiver to the HDDsystem 10 and its operator. Additionally, the distance of forwardadvance of the drill bit 18 without rotation can be determined at thereceiver assembly 36 and that information also transmitted from thereceiver to the HDD system 10. Such techniques are useful when boringon-grade boreholes or when desiring to bore to a point where thereceiver assembly 36 is positioned.

The present invention also contemplates an improved method forcommunicating information from the downhole tool assembly 24 to thereceiver assembly 36. As is well known in the art, the electronicspackage 30 in the downhole tool assembly 24 will generally comprisebatteries to provide operating power for the transmitter 32 and sensorsin the electronics package. However, the need to obtain reasonableoperating life from a battery-powered transmitter 32 gives rise to anumber of difficult engineering tradeoffs. The transmitter's 32 maximumoperating depth depends on many factors, but power dissipation in thetransmitter is a major—if not the dominant—consideration. Atransmitter's 32 operating life is also determined by the batterystack's energy capacity. Thus, the designer is forced to make acompromise between operating depth, which favors higher operating powerand shorter operating life, and operating life, which favors lower powerand reduced operating range. These are fundamental design tradeoffs forany battery-powered transmitter 32.

For improved performance, the present invention contemplates anadaptation of a data transmission technique known as Manchester coding.Other data transmission variants may have similar characteristics.Although the invention will be described in terms of Manchester coding,the invention may be used with any data transmission technique meetingsimilar data signal criteria.

Traditional serial digital transmission schemes commonly divide a datastream into small time intervals known as bit cells, data cells, or bitintervals, representing the amount of time needed to convey one bit ofbinary data. The simplest coding schemes rely on single-level signalsduring each bit cell. Other coding schemes use somewhat more elaboratewaveform constructs for specific reasons. For example, within a verycommonly-used family known as NRZ (Non-Return-to-Zero) codes there areeither zero or one transition in a bit period. Members of this codefamily are:

-   -   NRZ-L (-Level), in which a high level represents a “1” and a low        level represents a “0”,    -   NRZ-M (-Mark), in which a “1” is represented by a transition and        a “0” by no transition in the bit period,    -   NRZ-S (-Space), in which a “0” is represented by a transition        and a “1” by no transition in the bit period.        NRZ-L is seen to be the most common (and intuitive) of the data        codes.

This invention disclosed concerns a member of the Biphase code family inwhich there are at least one but no more than two transitions in a bitperiod. The particular code of interest is Biphase-L (-Level), in whicha “1” or “0” is represented by a level transition in the middle of thebit interval. Biphase-L is commonly known as Manchester or Manchester IIcode. Manchester II or Biphase-L code occasionally is further subdividedinto Bipolar One (logic “0” is defined as a low-to-high or rising edgetransition in the middle of the bit period, or Bipolar Zero (a logic “0”is defined as a high-to-low or falling transition in the middle of thebit period. The Bipolar One and Bipolar Two waveforms are logicalcomplements of one another and both are commonly made available byintegrated circuit devices which encode and decode Manchester datastreams. For simplicity, this disclosure refers to only “Manchester”code, which should be understood to represent all variants of the basiccode structure (whether known as Manchester, Manchester II, orBiphase-L). It is significant that Manchester code is self-clocking,which is to say data synchronization may be established and maintainedusing the fact there is a guaranteed transition at the midpoint of eachbit cell.

The primary advantages attending use of Manchester code in HDD trackingbeacons arise from the guaranteed transitions in the signal waveform.Equivalently, the signal waveform will be high for one half of each bitcell and low for the other half of each bit cell. In typical datatransmission applications, the high and low signal transactions involvetransitions between two different voltage levels. However, in HDDapplications this property may be used advantageously in at least twodifferent ways:

-   -   (1) by tuning the beacon transmitter on or off to represent a        signal condition (the “1” state) and a no signal condition (the        “0” state), respectively, or    -   (2) by frequency shifting the beacon transmitter frequency in or        out of a bandpass filter passband to represent the “1” and “0”        states, respectively. In other words, the in-band signal        frequency is generated during the high portion of the Manchester        waveform and an out-of-band signal frequency is generated during        the low portion of the Manchester waveform.        For simplicity, let alternative (1) be called Manchester/OOK        (Manchester On-Off Keying) and let alternative (2) be called        Manchester/FSK (Manchester Frequency Shift Keying).

Manchester/OOK coding is especially desirable. It guarantees the beaconsignal will be off half the time data is being transmitted, effectivelyresulting in a 50% power savings relative to frequency shift keyed (FSK)and phase shift keyed (PSK) data transmissions. Of equal importance,however, is the fact that the received signal amplitude may be simplyand accurately averaged over several bit cells while data is beingtransmitted. This simplifies the software needed to accurately determinedepth from transmitted data.

Manchester/FSK coding, on the other hand, provides no power savingsrelative to FSK or PSK transmission, but it does provide greateroperational flexibility. This arrangement presumes one or more digitalbandpass filters, each identified by different filter coefficients, andthe ability to generate a number of different FSK waveforms, alsodetermined by coefficients in software. The bandpass filter responsewill produce an output very similar to Manchester/OOK coding as the FSKsignal moves in and out of the bandpass filter passband. Although thereis no power savings, there is great operational flexibility—the operatormay select the operating frequency from a number of different frequencyand filter combinations to obtain the combination offering the bestoverall performance in the presence of local noise or otherinterference.

Turning to FIG. 14, another embodiment of the antenna arrangements foruse with the tracking system 22 (FIG. 2) is shown. FIG. 14 shows anantenna arrangement 200. The antenna arrangement 200 comprises a supportstructure 202. The support structure 202 is almost identical to thesupport structure 50 discussed above; however, support structure 202defines six channels 204 rather than three. As shown in FIG. 14, it ispreferred that each aperture area be defined by at least two channels204 existing side-by-side. The first and fourth channel 204A and 204Bdefine an aperture area. The second and fifth channels 204C and 204Ddefine an aperture area and the third and sixth channels 204E and 204Fdefine an aperture area.

The channels are orthogonally oriented such that the first and fourthchannels 204A and 204B are circumvented by the second and fifth channels204C and 204D and the second and fifth channels are circumvented by thethird and sixth channels 204E and 204F. A preferred embodiment for suchan arrangement comprises an orientation where a long side of therectangular second and fifth channels 204C and 204D is adjacent to andperpendicular to a short side of the rectangular first and fourthchannels 204A and 204B, and a diagonal of the rectangular third andsixth channel 204E and 204F is substantially coincident with a planeformed by the rectangular second and fifth channels 204C and 204D.

The size of the antenna arrangement 200 can be optimized by designingthe channels 204 such that the diagonal of the third and sixth channels204E and 204F intersects the plane of the second and fifth channels 204Cand 204D at an angle of between 0-10 degrees. Most preferably, thediagonal of the third and sixth channels 204E and 204F will intersectthe plane of the second and fifth channels 204C and 204D at an angle ofapproximately 4 degrees.

Continuing with FIG. 14, the antenna arrangement 200 further comprisessix antenna coils 206. The coils 206 may be insulated windings of litzwire. The coils may also comprise insulated windings of solid magnetwire. The six coils 206 are each separately wound around the structure202, one in each of the six channels 204A, 204B, 204C, 204D, 204E, and204F, to form six coil loops 206A, 206B, 206C, 206D, 206E, and 206F. Thecoils 206 do not intersect each other when positioned in the channels204. Preferably, the coil loops 206 are wound in a direction oppositethe loop directly adjacent to it. For example, coil loop 206A is woundopposite coil loop 206B, coil loop 206C is wound opposite coil loop206D, and coil loop 206F is wound opposite coil loop 206E. The coils 206may comprise 100-1000 turns of litz or magnet wire, though other numbersof turns may be used depending on wire size and antenna sensitivity orother design considerations. Preferably, each of the coils 206 maycomprise 300 turns.

Similar to antenna arrangement 42, due to the channel configuration, thecoil loops 206 all have coincident center points, and theirsensitivities are substantially identical. The coil loops 206 alsodefine substantially identical aperture areas and have rounded corners.Since the coils 206 are wound with litz or magnet wire, theirresistances are relatively low. Therefore, the antenna arrangement 200can be tuned properly to increase its sensitivity, thus allowing thetracking system 22 to detect the magnetic field from greater depths.

Turning to FIG. 14A, an alternative embodiment of FIG. 14 is shown. FIG.14A shows an antenna arrangement 201. The antenna arrangement 201comprises a support structure 203. The antenna arrangement 201 furthercomprises three channels 205A, 205B, and 205C. Each of the channels205A, 205B, and 205C holds an antenna coil comprising two windings 207Aand 207B. Thus, the antenna arrangement 201 comprises only threechannels 205A, 205B, and 205C with two windings 207A and 207B per eachchannel. The channels 205A, 205B, and 205C may comprise the samedimensions or different dimensions. The windings 207A and 207B may beadjacent to one another within each channel 205A, 205B, and 205C or thewindings may be intermingled within each channel. The winding 207A iswound opposite the direction of the winding 207B. The arrows in FIG. 14Adepict the direction of the windings 207A and 207B within each antennacoil. The windings 207A and 207B may comprise insulated windings of litzwire or solid magnet wire. A spacer 211 is also shown in FIG. 14A tohelp stabilize the windings 207A and 207B around the support structure203.

Referring now to FIG. 15, there is shown therein an alternativeembodiment for the antenna arrangement for use with the presentinvention. An antenna arrangement 208, shown in FIG. 15 is similar toantenna arrangement 200 except for that the third and sixth channels204E and 204F define an aperture area of a different dimension than thatof the first, fourth, second and fifth channels 204A, 204B, 204C and204D. While the dimensions are not identical, the third and sixthchannels 204G and 204H can be designed such that they define across-sectional area that is consistent with the cross-sectional area ofthe first, fourth, second and fifth channels 204A, 204B, 204C and 204D.Consistent cross-sectional areas will result in all of the coils 206wound within the channels 204 functioning substantially identically tothe embodiment shown in FIG. 14.

Turning to FIG. 16, the antenna arrangements 200 and 208 may be used asa plurality of antenna arrangements or they may be used individuallywith an alternative embodiment of the tracking system 22. Thealternative embodiment of the tracking system 22 may comprise theantenna arrangement 200 or 208, a frame 210, a ferrite rod antenna 212.When used individually the antenna arrangements 200 or 208 may besupported within frame 210 shown in FIG. 16. FIG. 16 shows antennaarrangement 208 supported by frame 210. The frame may also support theferrite rod antenna 212 and the receiver system (not shown). The ferriterod antenna 212 in combination with the antenna arrangement 200 or 208may allow the tracking system 22 to track and monitor the downhole toolassembly 24 at greater depths. A box comprising a handle (not shown) maybe used to enclose the frame 210 of the tracking system for use by theoperator during boring operations. The box may be configured to conformto the shape of the antenna arrangements 200 or 208.

In another embodiment, the antenna arrangements 200 and 208 may comprisea second antenna arrangement (not shown) remote from the frame 210 todetect the magnetic field source and send an antenna signal to theprocessor of the receiver assembly 36.

Various modifications can be made in the design and operation of thepresent invention without departing from its spirit. Thus, while theprincipal preferred construction and modes of operation of the inventionhave been explained in what is now considered to represent its bestembodiments, it should be understood that within the scope of theappended claims, the invention may be practiced otherwise than asspecifically illustrated and described.

What is claimed is:
 1. An antenna arrangement comprising: a supportmember comprising a first channel, a second channel, and a thirdchannel; wherein the first channel is disposed in a first axis, thesecond channel is disposed in a second axis, and the third channel isdisposed in a third axis; a first winding supported in the firstchannel; a fourth winding supported in the first channel and woundopposite the first winding; a second winding supported in the secondchannel; a fifth winding supported in the second channel and woundopposite the second winding; a third winding supported in the thirdchannel; a sixth winding supported in the third channel and woundopposite the third winding; wherein the first and the fourth windingdefine an aperture area, the second and the fifth winding define anaperture area, and the third and the sixth winding define an aperturearea; wherein the aperture area of each winding is the same; and whereineach of the windings have a common center point.
 2. The antennaarrangement of claim 1 wherein each of the windings comprise 100-1000turns.
 3. The antenna arrangement of claim 1 wherein each of thewindings comprise litz wire.
 4. The antenna arrangement of claim 1wherein each of the windings comprise solid magnet wire.
 5. The antennaarrangement of claim 1 wherein each of the channels has a rectangularprofile.
 6. The antenna arrangement of claim 1 wherein the first axis,the second axis, and the third axis are mutually orthogonal.
 7. Theantenna arrangement of claim 1 wherein the first channel is circumventedby the second channel and the second channel is circumvented by thethird channel.
 8. The antenna arrangement of claim 1 wherein a diagonalof the third channel intersects the first channel at an angle of between0-10 degrees.
 9. An antenna arrangement comprising: a first antenna coildefining an aperture area; a second antenna coil defining an aperturearea that circumvents the first antenna coil; and a third antenna coildefining an aperture area that circumvents the second antenna coil;wherein the first antenna coil, the second antenna coil, and the thirdantenna coil have a common center point; wherein the aperture area ofeach of the first, second, and third antenna coils are the same; andwherein each of the antenna coils comprise a first winding wound in afirst direction and a second winding wound opposite the first winding.10. The antenna arrangement of claim 9 wherein the first antenna coil,the second antenna coil, and the third antenna coil are mutuallyorthogonal.
 11. The antenna arrangement of claim 9 wherein each of thewindings comprise 100-1000 turns.
 12. The antenna arrangement of claim 9wherein each of the windings comprise litz wire.
 13. The antennaarrangement of claim 9 wherein each of the windings comprise solidmagnet wire.
 14. The antenna arrangement of claim 9 wherein the firstantenna coil, the second antenna coil, and the third antenna coil are asubstantially rectangular shape.
 15. An antenna arrangement comprising:a first antenna; a second antenna that circumvents the first antenna;and a third antenna that circumvents the second antenna; wherein thefirst antenna, the second antenna, and the third antenna have a commoncenter point; and wherein each of the antennas comprises a first printedcircuit board and a second printed circuit board facing opposite thedirection of the first printed circuit board to induce current flow in adirection opposite the first printed circuit board.
 16. The antennaarrangement of claim 15 wherein the first printed circuit board and thesecond printed circuit board each comprise a front side and a back sideand wherein the back side of the first printed circuit board is adjacentto the back side of the second printed circuit board.
 17. The antennaarrangement of claim 15 wherein the first antenna, the second antenna,and the third antenna are mutually orthogonal.
 18. The antennaarrangement of claim 15 wherein each of the antennas are substantiallyrectangular in shape.
 19. The antenna arrangement of claim 15 whereineach of the antennas comprise the same area.
 20. The antenna arrangementof claim 15 wherein the first printed circuit board and the secondprinted circuit board each comprise a plurality of connected layerscomprising windings.
 21. An antenna arrangement comprising: a firstantenna; a second antenna that circumvents the first antenna; and athird antenna that circumvents the second antenna; wherein the firstantenna, the second antenna, and the third antenna have a common centerpoint; wherein each of the antennas comprises a printed circuit boardcomprising a plurality of layers; and wherein a portion of the pluralityof layers induces current flow in a first direction and a second portionof the plurality of layers induces current flow in a direction oppositethe first direction.
 22. The antenna arrangement of claim 21 wherein thefirst antenna, the second antenna, and the third antenna are mutuallyorthogonal.
 23. The antenna arrangement of claim 21 wherein each of theantennas are substantially rectangular in shape.
 24. The antennaarrangement of claim 21 wherein each of the antennas comprise the samearea.